NEW YORK—This afternoon’s semifinal between world No. 1 Serena Williams and No. 6 Li Na, seeded fifth here, could be summed up by that old expression of wistful regret, “too little, too late.” Despite an entertaining, eleventh-hour surge by the underdog, Williams emerged with a lopsided 6-0, 6-3 win in one hour and 27 minutes.

The first third of the match’s lifespan was catastrophic for Li. Williams served first and pocketed the opening game in under two minutes with only one point extending into an actual rally, then broke her opponent in her first service game. Williams imposed herself on Li from the get-go, pushing her around the court (particularly way wide to the deuce court, where she was able to draw errors, or exploit the resulting open court), and when the two produced a rally, Williams—clearly the more self-assured of the pair this afternoon—usually outlasted her.

By the fourth game, Li—whose anguish was plain when her face was seen in close-up on the Jumbotron screens in Arthur Ashe Stadium—was self-destructing. She earned a much needed winner with a down-the-line backhand on the first point of her second service game, then double-faulted on the very next point as if to acknowledge that the concentration and resolution required to out-maneuver Williams was just too much. (In hindsight, however, that game was noteworthy for Li’s first serve-and-volley point of the match, a tactic that would be her redemption, if not her salvation, in the second set.) The rest of the opening chapter unspooled predictably and mercifully quick; 29 minutes after the match had begun, Williams had won her third straight bagel set and her 23rd consecutive game of the tournament.

To her credit, Li came back strong at the start of the second set, holding in her first service game to pull even at 1-1. She then, improbably, broke Williams, with some help from the defending champion, who began that game with a backhand that sailed wide, followed by a double fault of her own. In Li’s next service game, aided by a run of Williams unforced errors, she dashed out to a 2-1, 40-love lead, only to drop serve, allowing Williams to pull even at 2-all.

Once she had reestablished the upper hand, Williams never looked back… almost. With Li serving to stay in the match at 2-5, the two treated the fans to one of the most entertaining games of the tournament, a nearly 14-minute affair in which Li, letting her game fly for the first sustained passage of play all afternoon, saved six break points that were also match points, staying with Williams from the backcourt in extended rallies, and repeatedly venturing to net, where she either forced errors or was able to put away volley winners.

In the final game of the match, with Williams serving for the finals, Li made one last stand. At 30-0, with Williams serving, Li poked back a volley that had actually glided behind her, surprising Williams, who volleyed her reply into the net. The two then engaged in a slugfest of a point that Li won when her shot skidded off the baseline, throwing off Williams’ timing and visibly frustrating her. But the contest was over moments later when Williams drew a backhand long followed by, appropriately, a return that died in the net.

There was a lot of talk among the cognoscenti here that this might have been the match of the tournament on the women’s side. Li, according to Williams herself, has been moving great, and the two played a close match in Cincinnati three weeks ago in which both sets went to 7-5. On the other hand, their record coming into this match was 8-1 in favor of Williams, with Li’s lone win coming on hardcourt in Stuttgart five long years ago. And there was another daunting stat: This was Serena’s 24th career major semifinal, and she’d only failed to advance to the final in three prior attempts. What’s that thing Mary Carillo always says about if you want to take a Williams out of a slam, be sure to do it early?

Beyond all that, Williams is, as she has been all year, in take-no-prisoners mode, and though she showed moments of vulnerability, they didn’t last long and were righted with interest. Her opponent in the final, the No. 2 seed Victoria Azarenka, beat Williams in the Cincinnati final last month, but has looked shaky and anxious for much of this tournament; she’s dropped sets to Alize Cornet and Ana Ivanovic. Hers has been a B performance so far. Cincinnati seems much longer ago and farther away than it actually was. If Vika wants to avoid the same fate that has befallen the others who have taken on Serena these past two weeks, she needs to find her A game, and fast.

IBM Stat of the Match: A number of statistics tell the story of this ultimately one-sided affair, but I’ll go with Li’s encouraging 68 percent (13 of 19 points) success rate at the net as evidence of what might have been if she’d shown that aggression earlier. It might not have won her the match, but probably could have staved off the dreaded bagel.

IBM is a proud sponsor and official technology partner of the U.S. Open. For more information on this match, visit IBM's SlamTracker.